720921 has 8 divisors (see below), whose sum is σ = 977760. Its totient is φ = 472352.

The previous prime is 720913. The next prime is 720931. The reversal of 720921 is 129027.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 720921 - 2³ = 720913 is a prime.

720921 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (720901) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1860 + ... + 2213.

It is an arithmetic number, because the mean of its divisors is an integer number (122220).

2⁷²⁰⁹²¹ is an apocalyptic number.

It is an amenable number.

720921 is a deficient number, since it is larger than the sum of its proper divisors (256839).

720921 is a wasteful number, since it uses less digits than its factorization.

720921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4135.

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 720921 is about 849.0706684370. The cubic root of 720921 is about 89.6662950715. Note that the first 3 decimals are identical.

Adding to 720921 its reverse (129027), we get a palindrome (849948).

The spelling of 720921 in words is "seven hundred twenty thousand, nine hundred twenty-one".